Use of a star type LAN for connecting a plurality of end nodes to a line concentrator which is called a hub is now widespread. In this type of LAN, the hub is connected to each end node with stranded paired cables and modular jacks.
For example, 10Base-T which is described in the proposal of IEEE802.3 may be cited as such a LAN.
Recently in this star type LAN, developments for allowing the central line concentrator (hub) to control sending and receiving of a frame from downstream node and to arbitrate the transfer right thereof have materialized.
For example, in a system which is called a demand priority system in IEEE802.12, a medium access control (MAC) protocol provides that the hub arbitrates a frame transfer request from each downstream node which is connected to an intermediate hub, selects a downstream node, and gives permission for sending the frame.
This demand priority system will be explained hereunder. FIG. 19 shows a configuration example of a LAN to which the demand priority system is applied. In the drawing, numerals 200 to 207 indicate end nodes and 211, 212, and 213 indicate hubs. When an inter-network connection device such as a bridge is used so as to connect another network, the inter-network connection device is connected to the hub as an end node. In the drawing, 207 indicates an inter-network connection device. The hubs and end nodes are nodes of the LAN. In FIG. 19, those indicated on the upper part are upper-stream nodes.
In this LAN, a network can be configured by connecting a plurality of hubs hierarchically. 4-pair stranded cables are used for connection between the hubs and between the hubs and end nodes, that is, between the nodes.
Each of the hubs 211 and 213 has a plurality of downstream ports and an upstream port. The end nodes or the downstream hubs 211 and 213 are connected to the respective downstream ports of the upstream hub 212, and are regarded as downstream nodes of hub 212. The upstream hub 212 is connected to the upstream ports of the downstream hubs 211 and 213 and is regarded as an upstream node thereof. The uppermost stream hub 212 is called a root hub.
In each hub, the downstream ports to which the nodes which are required to transfer all the frames, such as the hubs and inter-network connection device, are connected, are set in the promise cure mode beforehand and the other ports are set in the privacy mode. To each port in the privacy mode, the address which is given to the node (end node) connected to the port corresponds. The promise cure mode is a mode for sending data to all of the nodes connected in the LAN and the privacy mode is a mode for specifying the node address and sending data only to the node which is defined by the specified address.
The frame transfer operation from the end node 200 will be explained hereunder with reference to FIG. 20.
The session for arbitrating the frame transfer right between the hub 211 and the end node 200 is executed by each using 2 pairs of the 4-pair cable for output and by alternately sending and receiving a control signal which is decided by a combination of 2 signal states on the 2-pair cable to be used for output as shown in Table 1. The same may be said with the hub 211 and the end node 201, 202, or others.
TABLE 1 ______________________________________ &lt;End node -&gt; hub&gt; &lt;Hub -&gt; end node Item TP1 TP2 Item TP3 TP4 ______________________________________ Receivable 0 0 Permission of 0 0 (Silence) sending (Silence) Idle 1 1 Idle 1 1 Transfer request NP 1 2 Request for 1 2 preparation of receiving (Incoming) Transfer request HP 2 1 Reserve (2 1) Training request 2 2 Training Idle 2 2 (for connection (for connection check) check) ______________________________________ 0: Silence 1: Tone1 (938 kHz) 2: Tone2 (1.875 MHz) NP: Normal Priority HP: High Priority
In the table, a symbol TP indicates a pair number of the stranded cable. As a signal state, three states such as the 938 kHz tone signal output state, 1.875 MHz signal output state, and silent state are used. The transfer request NP generally indicates a priority transfer request and the sending request HP indicates a top priority transfer request.
In the initial state, the hubs 211, 212, and 213 and the end nodes 200 to 207 which are connected to them output a control signal IDLE.
A case that a transfer request occurs in the end nodes 200 and 202 will be considered. Specifically, it is assumed that the end node 200 sends the transfer request HP and the end node 202 sends the transfer request NP to the hub 211. The hub 211 which recognizes it sends the control signal and the transfer request NP or the control signal and the sending request HP to the upstream hub 212 from the upstream port. When the hub 211 receives Silence from the upstream hub 212, it arbitrates the transfer right, selects the end node 200 for giving transfer permission so that the sending request HP works preferentially to the transfer request NP, and transmits Silence to the end node 200. The hub 211 sends the control signal and request for preparation of receiving (Incoming) to the other end nodes 201, 202, and 203.
The end nodes 201, 202, and 203 which receive the control signal and request for preparation of receiving from the hub 211, as shown in FIG. 20(2), always put the states of the self nodes into the Silence state immediately regardless of whether or not the respective nodes send a transfer request, and transmit Silence to the hub 211.
On the other hand, the end node 200 to which Silence is transmitted from the hub 211 recognizes permission of transfer and starts frame transfer to the hub 211 using all of the 4-pair wires. Since non-output is used as Silence in this protocol, no collision is generated during frame transfer.
The hub 211 which receives this frame sends the frame to the upstream hub 212 and checks the destination address of the inputted frame. When the end node which is the destination of this frame is connected, the hub 211 sends the frame to this end node using all of the 4-pair wires; The hub 211 also sends the frame to the node connected to the downstream port in the promise cure mode.
In the aforementioned operations, the operation of the upstream hub 212 which receives the transfer request from the downstream hub 211 is the same as the operation of the downstream hub 211 which receives the transfer request from the end node 200. However, the upstream hub 212 is a root hub and there is no upperstream hub thereof. Therefore, the hub 212 gives transfer permission to the node connected to the downstream port without waiting for transfer permission from the upstream hub and sends the request for preparation of receiving to the other downstream nodes.
The root hub 212 gives Silence to the hub 211 as mentioned above, sends the request for preparation of receiving to the hub 213 connected to the downstream port, and sends the frame received from the hub 211 to the hub 213 connected to the downstream port in the promise cure mode using all of the 4-pair wires.
When the hub 213 receives the request for preparation of receiving from the upstream hub 212, it sends the request for preparation of receiving unconditionally to each end node connected to the downstream port thereof. Thereafter, the hub 213 checks the destination address of the frame which is received from the upstream hub 212. When the end node which is the destination of this frame is connected, the hub 213 sends the frame to this end node using all of the 4-pair wires. The hub 213 also sends the frame to the node (in this example, the inter-network connection device 207) connected to the downstream port in the promise cure mode.
During the aforementioned operation, the hub 211 arbitrates the transfer right between the downstream nodes as described below. Namely, when the hub 211 receives Silence from the upstream hub, it selects one of the downstream nodes which send the transfer request by utilizing a round robin system, gives Silence to it, and sends the request for preparation of receiving to the other downstream nodes. For this selection, the transfer request HP works preferentially to the transfer request NP. The downstream node which is given Silence sends the frame, outputs IDLE, and abandons the given transfer right. The hub 211 which receives it outputs IDLE (1) to the remaining downstream nodes excluding the frame destination. When the transfer request is output from the other downstream nodes, the hub 211 selects one of the downstream nodes by utilizing the round robin system again, gives Silence to it, and sends the request for preparation of receiving to the other downstream nodes. When all of the downstream nodes are selected once by the round robin system in this way, the hub 211 sends IDLE to the upstream hub and abandons the given transfer right. However, the uppermoststream hub 212 is a root hub and there is no upper-stream hub thereof. Therefore, without waiting for transfer permission from the upstream hub and sending IDLE to the upstream hub, the hub 212 gives transfer permission continuously to the nodes which are connected to the downstream port thereof and outputs the transfer request by the round robin system sequentially.
When each hub except the root hub receives IDLE from the upstream node, it outputs IDLE to the upstream and downstream nodes. When each hub receives the transfer request from the downstream node thereafter, it outputs the transfer request to the upstream node.
As mentioned above, in the demand priority system, the interface between each node and the upstream node thereof is unified regardless of the end nodes and hubs, and each node other than the root hub operates according to an instruction by the control signal from the upstream hub according to the same protocol. In this protocol, the upstream hub has the control right for sending and receiving to and from the downstream node.
The correspondence between the protocol layer in the demand priority system and the protocol layer of the ISO and OSI reference model is shown in FIG. 21.
As shown in the drawing, in the proposal of IEEE802.12, the data link layer of the OSI reference model is divided into the logical link control sublayer (LLC sublayer) and the medium access control sublayer (MAC sublayer), and the physical layer of the OSI reference model is divided into the physical medium independent sublayer (PMI sublayer) and the physical medium dependent sublayer (PMD sublayer).
The upstream layer interface of the PMD sublayer is defined as a medium independent interface (MII).
Next, the conventional constitution of an end node is shown in FIG. 22.
As shown in the drawing, the end node generally consists of a LAN adapter 300 and a data processor 301 which uses the LAN via the LAN adapter 300.
The LAN adapter 300 has a PMD control unit 2, an MAC/PMI control unit 3, and an interface 302.
The interface 302 is an interface circuit between the LAN adapter 300 and the data processor 301.
The PMD control unit 2 bears the aforementioned PMD sublayer and the MAC/PMI control unit 3 bears the aforementioned MAC sublayer and PMI sublayer. In this constitution, an interface signal between the PMD control unit 2 and the MAC/PMI control unit 3 is defined as the aforementioned MII. The PMD control unit 2 has the predetermined mechanical and electrical structure and matches with a physical interface for sending and receiving a signal between the transmission line (a 4-pair stranded cable) and the control unit 2 . An interface signal between the PMD control unit 2 and the MAC/PMI control unit 3 is defined as the aforementioned MII.
The PMD control unit 2 converts a tone signal 24 which is input from the hub via a 2-pair stranded cable to a corresponding receiving state signal 7, transmits it to the MAC/PMI control unit 3, converts a plurality of sending state signals 8 which are sent from the MAC/PMI control unit 3 to corresponding tone signals 27, and outputs them to the hub via a 2-pair stranded cable.
On the other hand, as processing for the PMI sublayer, the MAC/PMI control unit 3 codes for the transmission line for a sending frame which is sent from the data processor via the interface 302 and decodes a receiving frame. Furthermore, as processing for the MAC sublayer, the MAC/PMI control unit 3 recognizes a control signal on the basis of a receiving state signal 7 which is sent from the PMD control unit 2, and generates a plurality of sending state signals 8 for realizing output of a control signal according to the aforementioned sequence. The MAC/PMI control unit 3 also controls sending and receiving of a frame according to the sequence of the recognized control signal.
For example, when a sending frame is sent from the data processor via the interface 302, the MAC/PMI control unit 3 recognizes that IDLE is sent from the hub from the receiving state signal 7, generates a sending state signal 8 for allowing the PMD control unit 2 to generate a tone signal corresponding to the transfer request, sends it to the PMD control unit 2, and recognizes the content of the control signal from the hub according to the kind of received receiving state signal, or absence thereof, which is received from the PMD control unit 2. When the received state signal is Silence, the MAC/PMI control unit 3 sends the coded frame to the hub which is connected via the PMD control unit 2, generates a sending state signal 8 for allowing the PMD control unit 2 to generate a tone signal corresponding to IDLE when the sending is finished, and sends it to the PMD control unit 2.
When the MAC/PMI control unit 3 receives a request for preparation of receiving from the connected hub via the PMD control unit 2, it generates a sending state signal 8 for allowing the PMD control unit 2 to generate a tone signal corresponding to Silence immediately, sends it to the PMD control unit 2, and transmits Silence to the connected hub via the PMD control unit 2. When the MAC/PMI control unit 3 receives a frame from the connected hub via the PMD control unit 2 thereafter, the MAC/PMI control unit 3 decodes it and sends it to the data processor 301 via the interface 302.
Next, the constitution of the hub will be explained.
As shown in the drawing, the hub consists of a PMD control unit 2 which is installed on each of the downstream port, upstream port and a frame send receive controller/transfer right arbitrator 303.
The PMD control unit 2 of the hub is at the same position as the PMD control unit 2 which is on an end node. The frame send-receive controller/transfer right arbitrator bears processing for the MAC sublayer and PMI sublayer in the same way as with the aforementioned MAC/PMI control unit 3 which is an end node and as with processing for the PMI sublayer, and it codes for the transmission line for a sending frame which is sent from the data processor and decodes a receiving frame. Furthermore, as processing for the MAC sublayer, it recognizes a control signal from a receiving state signal, generates a tone source signal for each port according to the aforementioned sending and receiving sequence and the transfer right arbitration system, controls sending and receiving of a frame according to the retransfers a frame betal, and transfers a frame between the ports according to the aforementioned frame address and the mode and kind of each port (downstream port and upstream port).
As mentioned above, in the demand priority system, each of the end nodes sends or receives a frame according to an instruction of the hub.
Therefore, when the end nodes are directly connected to each other, they will not operate normally.
For example, when transfer requests NP conflict with each other between end nodes which are directly connected, both of them recognize it as a request for preparation of receiving (Incoming) from the hub, so that all the end nodes output Silence and transfer to the reception waiting state.
When one of the end nodes sends a transfer request HP, the signal is ignored because it is not defined on the end node side which receives it.
On the other hand, when two hubs in which end nodes are connected to all of the downstream ports are connected to each other, one more hub is necessary as an upstream device. However, such a hub is not inexpensive, so that when 2 or 3 end nodes are to be connected to each other or end nodes which are larger by one than the number of downstream ports of the hub are to be connected, it is desirable from a viewpoint of cost and system scale that the end nodes can be directly connected to each other in place of one more hub being prepared. Also when end nodes in the same quantity as the number of downstream ports of a plurality of hubs are to be connected, it is desirable that the plurality of hubs can be directly connected to each other without one more hub being prepared as an upstream hub, or root hub, of the plurality of hubs.
This problem can be solved by newly developing a MAC protocol which enables direct communication between end nodes or hubs, and by installing a function for realizing the MAC protocol in each end node or hub. However, by doing this, the system, particularly the function of each end node becomes complicated and an inexpensive LAN cannot be realized.